1. Field of the Invention
The present invention is directed to an improved inflatable radar reflector. Specifically, it is directed to improved geometry for the shape of the inflatable envelope, the shape of the internal reflectors, and the means of suspension by which the reflectors are deployed to accurate planar alignment.
2. Description of the Prior Art
The effectiveness of radar detection is related to the effectiveness with which a radar source signal may be reflected from an object, i.e. a radar reflector. Radar reflectors may be utilized for air/sea rescue, vessel avoidance, marking of temporary runways, designation of hazardous areas, etc. In such an application, the larger the radar cross-section of the reflector, the better. The successful incorporation of an effective corner reflector array into an inflatable device has been found to provide a radar cross-section which is many times larger than an object the same size without a corner reflector array.
Corner reflector arrays have been designed which are included in an inflatable assembly having flexible or collapsable internal corner reflectors that may be folded into extremely small volumes, such as into the pocket of a life vest, so as to be easily stored. The corner reflector array may reside in a flexible material which is resilient and not easily damaged. The corner reflector array residing inside an inflatable flexible envelope insures that the reflector may not be bent out of shape or otherwise functionally impaired, even during severe use. The inflatable reflector may be inflated orally or with compressed air or with lighter than air gas.
Previous patents of the prior art have addressed the design of inflatable corner reflector systems. Such examples may be seen in U.S. Pat. Nos. 2,463,517; 3,103,662 and 3,115,631. However, due to the method of construction of inflatable radar reflectors of the prior art, the corner reflector arrays thereof are distorted substantially reducing their effectiveness as radar reflectors, particularly for modern day radar systems utilizing shorter wave lengths.
U.S. Pat. No. 4,673,934 discloses a much improved inflatable radar reflector in which the corner reflector array thereof is constructed and attached in such a manner that the reflectors are held taut and flat and in proper orthogonal orientation significantly reducing puckers, sags, twists or angular misalignment inherent in prior art designs. This results in an inflatable radar reflector of significantly greater radar cross section enhancement.
In many inflatable radar reflector applications, a compressed gas supply is required for automatic inflation. The weight and volume required for the inflation system may be larger than the weight and volume of the stowed radar reflector. For this reason, the volume of an inflatable radar reflector is a limiting design consideration. The effectiveness of an inflatable radar reflector is thus significantly enhanced if the volume required for a given radar cross section can be minimized.
In essentially all of the prior art inflatable radar reflectors, a plurality of triangular reflectors are arranged in a tetrahedral array forming eight corner reflectors which are suspended in a spherical inflatable envelope. It has also been found that the spherical-triangular-tetrahedral geometry limits the radar cross section which may be obtained per unit of volume.